The increasing cost of petroleum products, together with the society's demand for industrial practices that do not harm the environment require constant development of the lubricant market. In this sense, the incorporation, to a lubricant oil, of solid nanoparticles of a lubricant lamellar material, makes said nanoparticles act as a friction modifying additive which also improves the lubricity and lifetime of the lubricant oil.
Said incorporation of solid lubricant nanoparticles to a lubricant oil may dispense the use of other synthetic chemical additives, which are typically used to increase the viscosity and chemical stability of lubricant oils, allowing the use of low-viscosity oils and leading to economic gains.
The molybdenum disulphide (MoS2) is a lamellar material with a weak interaction between its layers, which fact makes it be widely used in solid lubrication in vacuum or in the absence of oxidant agents, as water vapor and oxygen, as well as mixed in greases and oils (A. R. Lansdown, Molybdenum Disulphide Lubrication, Tribology Series 35, Elsevier 1999).
The molybdenum disulphide (MoS2), in its microcrystalline form, does not disperse in oil neither in water. That is why its applicability as additive in mixed lubrication has to overcome this technological difficulty. When in the nanometric dimension, this difficulty can be overcome by functionalizing (sometimes also characterized as capping) the nanoparticles of molybdenum disulphide (MoS2) through a second reagent, of the family of thiols, phosphines, dithiocarbamates and the like, most of all harmful to the environment. Thus, it can be formed very stable suspensions of MoS2 nanoparticles in oils, constituting a mixed lubrication product with significant gains in lubricity. However, these reagents, as they become worn under friction, will almost always produce secondary reactions with the lubricant oil, causing its consequent premature degradation. The present invention brings a new approach for the dispersion of MoS2 nanoparticles without the need of these aggressive capping agents.
The transformation of the MoS2 nanoparticles in hydrophilic particles, made with friendly capping agents, makes it possible to use them as additive in pure water, forming a new type of mixed lubricant appropriate for mild regimes, in which the uncoupling of the capping agent does not occur.